Examples of application of a transparent plastic product having a glare-reducing ability include windows for construction, sunroofs and windows for motor car, sun glasses, goggles, illuminations and ornaments.
Particularly, recently, demand for plastic lenses used a transparent aromatic polycarbonate with excellent impact resistance in a sun glass with degree having a glare-reducing ability has rapidly expanded mainly in U.S.A. Thus, lens materials for spectacle having more excellent optical properties than those in an aromatic polycarbonate have been extensively developed.
For example, Japanese Patent Kokai (Laid-open) No.12-63506 discloses that an aromatic-aliphatic copolymerization polycarbonate resin material has balanced and excellent optical properties as a lens material. When an object is seen through a lens applied this material as a lens base material, Abbe's number representing definition of image (Abbe's number: a value representing a degree of color aberration of a lens material) is higher as 39 than 29 of conventional aromatic polycarbonate, so that definite image can be seen.
Further, the refractive index of this material is 1.57 whereas conventional polymethylmethacrylate as an optical material is 1.49. This material has a high refractive index about equivalent to 1.59 of conventional aromatic polycarbonate. When this material is applied to a spectacle lens with degree, it is suitable to a spectacle lens requiring lightness because its thickness can be made thin.
A sunglass with a polarization property has a glare-reducing ability excellent in cutting characteristic against a reflected light. Thus, its usefulness in outdoor activities such as marine sport, skiing and fishing has come to be noticed widely. Recently, its demand has rapidly expanded. Particularly, when it is produced from an aromatic polycarbonate, the above-mentioned tendency is remarkable because it is excellent in impact resistance.
On the other hand, with progress of rapid development for excellent photochromic pigment, a plastic photochromic sunglass with a glare-reducing ability changing transmittance depending on surrounding brightness has been remarkably improved and is rapidly attaining popularity.
However, it is not easy to process the plastic photochromic sunglass. For example, in the production of such polycarbonate lens as described in Japanese Patent Kokai (Laid-open) No.61-5910, when a process comprising adding a photochromic pigment(s) during production of a polycarbonate sheet to be used is applied, a lens thus obtained is insufficient in both response speed and contrast. Also in resins other than polycarbonate, there usually occur some problems that, in a sheet with strength usable as a glare-reducing material, degradation of a photochromic pigment occurs; its kneading is troublesome; contrast of a product to be obtained is low and its response speed is slow.
Further, in a lens base material, when aromatic polycarbonate is applied to the base material, definition of image is, as described above, slightly inferior because its Abbe's number is comparatively small and interior distortion becomes large due to its high photoelastic constant. Therefore, further improvement of optical properties has been desired.
Thus, development of a lens material used a polycarbonate excellent in impact resistance as a lens base material in which distortion of image is small and definition can be secured has been required. Moreover, further improvement of performances of a lens with a glare-reducing ability due to a polarization property or a photochromic property changing transmittance depending on surrounding brightness has been required.